This invention relates to the cutting of ultra-hard materials.
Ultra-hard materials are those which themselves have a high hardness, e.g. particles which have a hardness of about 10 or more on the MOHS hardness scale, or materials which contain such particles and have a similar hardness. Particular examples are natural or synthetic diamond and cubic boron nitride, or polycrystalline diamond (PCD) or polycrystalline cubic boron nitride (PCBN).
Ultra-hard materials, particularly those of synthetic nature, can be produced in relatively large sizes and need to be cut for various applications. For example, PCD can be produced in the form of a large disc and this disc needs to be cut into smaller pieces, such pieces having application, for example, as drill or cutting inserts. Further, diamond plates produced by chemical vapour deposition (CVD) are cut into smaller pieces for use as heat sinks for semiconductor devices or in mechanical applications.
Various methods have been used in the past for cutting ultra-hard materials. Examples of such methods are spark erosion, and laser cutting. Laser cutting has traditionally used rod lasers which have the disadvantage that damage to the ultra-hard material generally occurs. This damaged material has to be subsequently removed. This removal adds to the expense of producing a product from the ultra-hard material and is wasteful of the material itself.
According to the present invention, a method of cutting an ultra-hard material includes the steps of using a slab laser beam to effect the cut. By xe2x80x9cultra-hard materialxe2x80x9d as used herein and in the claims is meant a particle which has a hardness of about 10 or more on the MOHS hardness scale, or a material which contains such particles and has a similar hardness. Particular examples of such materials are natural or synthetic diamond and cubic boron nitride polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (PCBN).
The invention uses a slab laser. A slab laser may comprise a slab of material having parallel, elongate faces and end faces which are each cut to define a brewster angle. The laser beam enters and exists across the brewster angle end faces and undergoes total internal reflections on the two parallel, elongate faces. This reduces the thermal distortion and lensing effect leading to reduced beam divergence. Restricting the laser to oscillate in TEM00 mode only further reduces the beam divergence. This results in a xe2x80x98sharperxe2x80x99 more parallel beam with greater depth of focus which is beneficial to precision laser cutting of ultra-hard materials. In addition, the greatly reduced beam divergence means that a smaller spot size (focussed spot) is possible.
It has been found that the use of a slab laser improves cutting efficiency and reduces damage to the ultra-hard material. Thus, a higher yield of smaller products or pieces from the material is possible than when using a rod laser. A slab laser further allows for better heat distribution and lower power use.
The use of a slab laser has application in any ultra-hard material, particularly a backed or an unbacked PCD or PCBN. A backed PCD or PCBN comprises a layer of PCD or PCBN bonded to a substrate or support which is generally a cemented carbide. The cemented carbide may be any known in the art such as cemented tungsten carbide, cemented titanium carbide or cemented tantalum carbide.
In use, the slab laser may be used to produce a cut completely through the ultra-hard material producing two or more separate pieces. Alternatively, the cut may be only partially through the material, from one or both sides.
The invention has particular application to the cutting of backed or unbacked PCD or PCBN. It has been found that the slab laser on cutting through the PCD or PCBN allows for weak graphite or hexagonal boron nitride bonds, as the case may be, to be formed leaving a weakly bonded structure. With carbide backed PCD or PCBN, weak carbide bonds are also formed in the carbide backing. Further damage to the PCD, PCBN and carbide backing is less with slab laser cutting when compared with rod laser cutting.